Hello Sotrured. Welcome to the HP Forums. I understand you are experiencing audio installation issues. Thank you for the detailed post, it is truly appreciated. I know what troubleshooting has been done, and I know what to tell you.
I've noticed that you have not reinstalled the operating system. If the issue is software-related, reinstalling Windows Vista should resolve the issue. For more information on how to do this, please reference this Microsoft website: Installing and reinstalling Windows
If this does not resolve the issue, the computer could be experiencing a hardware issue. This is the only possibility that I can think of, based on the information provided.
Please respond as soon as you can. I will continue to research the issue.
Mario